Purpose of the study: Acetabular version is a most important parameter for repositioning the acetabular fragment during periacetabular osteotomy. Recently, a few studies have presented a significant number of dysplastic hips with acetabular retroversion. There have not however been any studies devoted specifically to the severity of bilateral acetabular retroversion. The purpose of this work was to determine the incidence of bilateral retroversion in patients undergoing periacetabular osteotomy for dysplasia in order to identify and validate a retroversion index which would be predictive of the degree of retroversion. This index could be added to congenital hip dysplasia classifications to include acetabular version.

Material and methods: The Lequesne lateral view of the hip was obtained in 174 patients (348 hips, 137 women and 37 men, mean age 30 years) undergoing periacetabular osteotomy for symptomatic dysplasia. One hundred ninety-five hips (56%) were operated on and 153 (44%) were considered normal or non-symptomatic and were not operated. The following parameters were noted for each hip: VCE, VCA, HTE, femoral head extrusion, index of acetabular depth, crossing-over, retroversion index. The retroversion index was checked on a bone model of the pelvis which was x-rayed in the neutral position then turned progressively. Statistical data were analyzed with SAS.

Results: Five percent of the operated hips presented neutral version, 53% anteversion and 42% retroversion. Twenty-four percent of the non-operated hips were normal, 22% presented pure retroversion and 54% were dysplastic. All of the measurements were significantly deviated towards dysplasia for operated hips, with the exception of the retroversion index and the VCA.

Discussion: These data validated the retroversion index and confirmed that one out of three dysplastic hips displays retroversion. In addition, it would appear that for dysplastic hips with retroversion, the degree of lateral coverage or the HTE angle determines whether surgery is needed or not and not the degree of retroversion. But as pure retroversion can be symptomatic in itself, and since the majority of these version or cover anomalies can be treated by periacetabular osteotomy, we propose a classification of hip dysplasia included acetabular version.

Conclusion: This classification is designed as an aid for the orthopedic surgeon for reorienting the acetabular fragment to obtain the optimal position.